Ms. Scholl, RECURSIVE EXACT RAY TRACE EQUATIONS THROUGH THE FOCI OF THE TILTED OFF-AXIS CONFOCAL PROLATE SPHEROIDS, J. mod. opt., 43(8), 1996, pp. 1583-1588
Simple, exact ray trace equations are derived for a general ray propag
ating through the foci of tilted, coupled, confocal spheroids. In this
off-axis optical system, there does not necessarily exist a (real) ra
y for which the paraxial approximation applies.